A rigid endoscope having a relay optical system has been known as this kind of endoscope (see Patent Document 1).
The rigid endoscope has a cylindrical insertion unit made of a rigid member, a relay optical system (relay lens system) provided in the insertion unit, an observation unit provided at a base end portion of the relay optical system, two light guide optical fiber bundles provided with the relay optical system in the insertion unit and a light source device connected to a base end of the two light guide fiber bundles.
The light source device is activated, and illumination light from the light source device is guided by the light guide fiber bundles and is illuminated on an object (examined body) as observation target from a tip end thereof. Reflected light from the examined body forms images at the observation unit and the images are observed by the naked eyes through the observation unit.
[Patent Document 1] JP 2007-133175A